I. Field of the Invention
The present invention relates generally to hemming machines and, more particularly, to an inside perimeter hemming machine.
II. Description of the Prior Art
There are many previously known inside perimeter hemming machines of the type used to form an interior hem on a manufactured part, such as an automotive door panel. These previously known interior hemming machines typically comprise a base and a nest which is vertically movably mounted relative to the base. The nest supports the workpiece or part to be hemmed and is vertically movable by actuators to predetermined vertical positions relative to the base.
In order to form the hem, typically two die sets are pivotally mounted to the base and movable between an operative position and an inoperative position. In their operative position, the die sets overlie the workpiece so that, upon vertical movement of the nest, the workpiece carried by the nest impacts upon the die sets to form the prehem and then final hem. Conversely, in their inoperative position, the die sets are pivoted away from the nest so that the nest can be vertically displaced without interference from the die sets.
Typically, a first die set forms a prehem, i.e. the metal forming the hem is bent at approximately a 45xc2x0 angle. After the prehem is formed, the prehem die set is moved to its inoperative position and the other or final hem die set is moved to its operative position also overlying the workpiece on the nest. The nest is then vertically displaced against the second die set which forms the final hem on the workpiece.
In forming an interior hem around a workpiece such as a door panel, the interior hem is formed around three sides of the workpiece. In order to produce an acceptable hem, the previously known interior hemming machines have utilized both a prehem and final hem die set which, when in their operative position, extend continuously around the three sides of the workpiece to be hemmed. This has necessarily entailed overly complex and therefore expensive constructions for both the prehem and final hem die set. Furthermore, the mechanism utilized to pivotally move the prehem and final hem die sets to the base imposes a nonlinear relative motion between the nest and dies, and present and angular deflection when applying the final hemming force, which will affect the geometrical quality of the hem.
The present invention provides an inside perimeter hemming machine which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the interior hemming machine of the present invention comprises a base which is adapted to be supported by a ground surface. A nest is vertically movably mounted to the base and this nest is adapted to support the workpiece, such as a door panel, to receive the interior hem. An appropriate actuator, such as a hydraulic or electric actuator, is then utilized to vertically displace the nest together with its supported workpiece between predetermined vertical positions relative to the base.
A die assembly housing is also mounted to the base such that the die assembly housing is positioned within the opening of the workpiece around which the interior hem is to be performed. For example, in the case of an automotive door panel, the die assembly housing would be positioned through the window opening. Furthermore, in this case, the hem would be performed around both sides and the top of the window opening.
At least two die sets and preferably three die sets are horizontally slidably mounted to the housing so that the die sets are movable between an extended and a retracted position. Each die set, furthermore, is vertically spaced from the other two die sets. One die set is utilized to perform the prehem, the second die set performs the final hem along most of the length of each of the three hemmed sides of the workpiece, while the third die set forms a final hem on the corners of the workpiece. A fourth die set can be easily added to perform the corner hem in two stages rather than one.
In order to horizontally move the die sets between their extended and retracted positions, at least one wedge drive member is associated with each side of the die set and these drive members each include a drive surface which lies on a plane skewed with respect to the direction of movement of the nest. Consequently, for a three sided interior hem of the type typically formed on an automotive door panel, the prehem and final hem die sets each have three drive members although the drive members in each set may be of a one-piece construction. At least one driven member is then associated with each drive member wherein each driven member includes a skewed surface which flatly abuts against the skewed surface of its associated drive member.
The die assembly housing constrains the driven members against vertical movement. Consequently, vertical displacement of the drive members horizontally moves the driven members together with their attached die sets between the extended and the retracted positions. In order to vertically displace the drive members, preferably a conventional pneumatic or hydraulic cylinder can be used to move the shaft up and down. Consequently, as the shaft is vertically moved by the cylinder, the drive members are horizontally displaced either in or out depending upon the direction of movement of the shaft.